1. Field of the Invention
The present invention relates to a capsule endoscope that is inserted into a subject and picks up an image inside the subject, and to a capsule endoscope system for the same.
2. Description of the Related Art
In a field of endoscopes, a swallowable type capsule endoscope has been proposed in recent years. The capsule endoscope has an imaging function and a radio transmission function. During a period from when the capsule endoscope is swallowed from a mouth of a subject for an observation (inspection) until when the capsule endoscope is naturally discharged, the capsule endoscope travels through inside a body cavity, i.e., inside organs such as a stomach and a small intestine, and sequentially images inside the organs, while following peristaltic motion of the organs.
Image data obtained inside a body by the capsule endoscope is sequentially transmitted to outside by radio transmission and stored in a memory provided outside, while the capsule endoscope travels through inside the body cavity. The subject can freely move during the period from when the capsule endoscope is swallowed until when the capsule endoscope is discharged, since the subject carries around a receiving device that has the radio transmission function and a memory function. After the capsule endoscope is discharged, a diagnosis can be made by a doctor or a nurse by displaying the image, which is based on the image data stored in the memory, of the organs on a display.
The imaging function provided in the capsule endoscope is realized by, for example, a predetermined optical system and an imaging element such as a charge-coupled device (CCD). Specifically, the capsule endoscope acquires the image inside the subject by converting incident light focused by the optical system to electronic signals.
However, the conventional capsule endoscope system has a problem in which it is not easy to acquire a high quality subject interior image. Specifically, in the conventional capsule endoscope, it is difficult to acquire the high quality subject interior image due to difficulties in an adjustment of illumination luminance of the capsule endoscope and presence of noise components in acquired image data. Hereinafter, the problem is described in details.
The conventional capsule endoscope has a problem in which it is not easy to adjust illumination light intensity of a light emitting diode (LED). Since the capsule endoscope needs to be miniaturized to a size insertable into the subject, it is preferred also to simplify a circuit installed in the capsule. Further, since the capsule endoscope needs to be driven for, for example, substantially 8 hours from when the capsule endoscope is inserted into the subject until when the capsule endoscope is discharged, a controlling circuit and the like provided in the capsule endoscope is required to have low power consumption.
Therefore, it is not realistic at least at the present moment to install a photochromatic mechanism, which is provided, for example, in a digital camera, in the capsule endoscope, so that it is necessary to provide a photochromatic mechanism specialized for the capsule endoscope. However, among the photochromatic mechanism proposed at the present moment, a photochromatic mechanism suitable for a use condition of the capsule endoscope does not necessarily exist.
A problem in which the noise components due to dark current are included in the image data will be described. The dark current is a current component caused independent of incident light, and caused due to a mechanism of an imaging element such as the CCD. The noise components are mixed into an acquired image data corresponding to an amount of the dark current.
FIG. 7 is a schematic graph of one example of temperature dependency of the dark current. As shown in FIG. 7, strength of the dark current tends to monotonously increase as the temperature rises, and the noise components caused due to the dark current increase along with the rise in environmental temperature.
Since the capsule endoscope performs an imaging operation inside the subject, the environmental temperature of the capsule endoscope becomes approximately 38° C. (Celsius). When the imaging element such as the CCD is used under such a temperature condition, the dark current increases to substantially 3 to 4 times an amount under a room temperature (for example, 20° C.). Therefore, when the imaging operation is performed by using the imaging element provided in the capsule endoscope, the amount of the dark current increases compared to when a normal imaging device is used, and the quality of the image is largely affected.
A configuration in which an imaging is performed while cooling the CCD to eliminate the influence of the dark current has been proposed, and some have already put the configuration into practical use. However, to install the cooling mechanism in the capsule endoscope is not appropriate since the cooling mechanism consumes large electric power, and currently, other alternative units do not exist.